Dell sells this device with Ubuntu 11.10 pre-installed as well and the Ubuntu certification programme for the Vostro 2520 states it is only certified with this preinstalled image. Please check the Dell support page for any hints on this - they may have a fix/package/article about this for Ubuntu. These media keys should be working out of the box with regular media players. Can you check this with the Ubuntu default player?
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gertvdijkFeb 4 '13 at 12:04

As of update 2 - would there be any suggestions about mp3 players ?
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ElmorFeb 5 '13 at 10:51